Yes, there are several diff lockers available. Truetracs, detroits, ashcroft air lockers, arb air lockers, I think kaiser and TJM have them too. Some like the detroit and truetrac are activated automatically when traction is lost, some are electronically activated, and the ashcroft and arb are activated by bursts of air from a compressor. There are VERY HIGH cost with air lockers because you need the compressor, air lines, lockers, and you should upgrade gearing and HD axles/ cv joints. You can also damage your vehicle very easily with lockers, as they'll take you up things you may not want to travel back down.

 

Whoa there...yes they're available, but what are you looking to do with the truck? There are air lockers, detroit lockers, Tru-track limited slip diffs...

You have options, but it sounds like you need to slow down, decide what you want to do, then read up on all of the various options and combinations. When you start looking at lockers, you need to start thinking about replacing axles, CV's and other parts too...